The present invention relates to an error compensation apparatus for precision machines and measuring instruments, and more particularly to a correction apparatus for use with an encapsulated longitudinal measuring instrument adapted for measuring the relative position of two objects, such as the bed and the carriage of a precision machine tool.
Various types of correction systems for the compensation of measurement errors are known in the prior art. For example, German Patent DE-PS No. 866 402 describes a measuring system having a correction ruler whose cursor is mechanically adjusted by an amount corresponding to the prevailing error of the spindle with reference to the ruler. A position measuring system with a correction pattern is described in U.S. Pat. No. 3,039,032, which is scanned by a sensor which directly acts on the transmitter of the reading (rotary transmitter). German DT-AS No. 1 231 595 discloses an apparatus for the remote electrical indication of the movements of a mobile machine component where a system is used which has a deformable metal tape which is scanned by a transmitter for the compensation of errors. Another error correction system is described in German DT-OS No. 2 042 505 in which the numerical measuring system of a machine is provided with an additional movement commensurate with the prevailing value of the error of the machine spindle by a scanning means which reads a correction stencil.
In part, the afore-mentioned correction systems are relatively complex systems which require additional electrical adjustment apparatus or rotary transmitters or which are coupled directly to the machine. However, in all cases their construction is relatively expensive and the cost of such systems precludes their use in many applications.